Exhaust gas recirculation has been employed since the mid 70's for air-breathing, spark ignition gasoline engines and since the early 2000's for heavy duty diesel engines. The purpose of EGR is to increase the nitrogen gas content in the combustible mixture to reduce combustion temperatures and accordingly the production of oxides of nitrogen which are considered to have harmful affect on the environment. A typical system involves a valve that allows a predetermined proportion of the exhaust gases to be directed to a mixer somewhere in the air inlet of the engine. Typically, a flow meter is incorporated in the system to more precisely control the flow of EGR relative to the air delivered to the inlet of the engine.
A problem with systems of this type is that internal combustion engines having multiple reciprocating pistons connected to a common exhaust manifold do not produce smooth uniform exhaust discharge, but rather a series of pulses that occur when the individual exhaust valve or valves are opened. Accordingly, the exhaust flow taken off for EGR is not a steady state stream but a series of pulses. When these pulses are directed to the engine air inlet they can be out of phase with the opening of the intake valves and cause an imbalance in the percentage of EGR between cylinders of the engine. Further, venturi flow meters operating on the Bernoulli Principle can have variations in results because of the pulsed rather than steady state flow through the meter.
Accordingly, a need exists in the art to provide relatively consistent and predictable EGR flow.